Ethernet links are used to connect devices to form a network to exchange data. Ethernet links are specified to operate over a number of transmission media such as co-ax cable, fiber optic cable, and twisted-pair cable. Ethernet links are also specified to operate at a number of data rates such as 10 megabits per second (Mb/s), 100 Mb/s, 1 gigabit per second (Gb/s), 10 Gb/s, 40 Gb/s, or 100 Gb/s, for example. A number of Ethernet physical layer entities (PHY) types are specified using various encodings to support the various transmission media, data rates, and distances. In the case of twisted-pair cable used for Ethernet links, the twisted pair cable comprises eight wires in the cable formed into four balanced twisted-pairs. In the case of fiber optic cable used for Ethernet links, there may be one, two or multiple of either single-mode or multi-mode fibers in the cable. The Institute of Electrical and Electronics Engineers (IEEE) 802.3 Ethernet standard defines a function termed “auto-negotiation” for passing configuration information from one PHY to another PHY on a link as part of the link start-up sequence. Auto-negotiation provide for the PHYs at the ends of an Ethernet link to exchange their abilities and then commence operation at their highest common operating ability. Auto-negotiation is specified for operation on twisted-pair as well as certain fiber optic links.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.